JOHANNESBURG, South Africa (AP) _ An American missionary couple said Friday the government ordered them to leave the country by next week.

The Reverends Brian and Susan Burchfield of the American Lutheran Church said an official of the Ministry of Home Affairs handed them a letter Thursday night informing them of their expulsion.

''No reason was given,'' said Mrs. Burchfield, 39, in a telephone interview. ''There are no charges pending against us anywhere and so we are completely in the dark. Our work permit was recently renewed until Oct. 9.''

The Burchfields were sent from Lynnwood, Wash., on their first overseas post in January to help a Cape Town pastor with his congregation of 600 mixed- race South Africans.

The letter said only that Home Minister Stoffel Botha ''has considered it to be in the public interest to order your removal from the republic.''

The Burchfields, who came to this country with two daughters, were told they could appeal by Wednesday, but would have to leave by midnight Thursday if the appeal failed.

The couple were among 56 people arrested on a disorderly conduct charge March 7 while saying goodbye at the airport to a deported Lutheran minister, Gottfried Kraatz.

Burchfield, 38, was among 250 people detained June 15 at St. Nicholas Anglican Church following a memorial service for blacks killed in the 1976 Soweto riots. He was released without charge after three hours.

''One of the people in our congregation also happened to be detained in St. Nicholas and we see pastoring here as we would in the United States. If someone in your congregation is hurting, in hospital or prison, you not only visit them but you work on behalf of their well-being, if it's inquiring about their condition or getting them legal help,'' said Mrs. Burchfield.

''I think it's a good example of how someone can be arrested, detained, deported for any number of ridiculous reasons. If we're deported, I'm not going quietly,'' she said.

Groups monitoring detentions say hundreds of people have been held since the state of emergency was declared June 12.